1. Field of the Invention
The present invention relates to a method of generating cracks in a polycrystalline silicon rod so as to crush the polycrystalline silicon rod into lumps.
Priority is claimed on Japanese Patent Application No. 2009-175441, filed on Jul. 28, 2009, the content of which is incorporated herein by reference.
2. Description of Related Art
Czochralski method (CZ method) is used to produce single crystal silicon for semiconductor devices. In the CZ method, lumps of polycrystalline silicon are installed in a crucible and molten in the crucible, and a single crystal silicon is pulled up from the silicon melt.
The polycrystalline silicon can be produced by Siemens method. Since a rod-shaped body of polycrystalline silicon is formed in the Siemens method, it is necessary to process the rod into lumps of appropriate size so as to install the polycrystalline silicon in the crucible efficiently. The polycrystalline silicon rod is a brittle material and is crushed to fragments of appropriate size using a hammer or the like. In a technique conventionally known, the polycrystalline silicon rod may be subjected to a preliminary treatment to generate cracks in the rod before crushing the rod. In the preliminary treatment, a heated polycrystalline silicon rod is quenched by immersing the rod in pure water, thereby causing thermal strain in the silicon rod. As a result, cracks are generated in the polycrystalline silicon rod.
For example, PCT International Publication, WO2009/019749 describes an apparatus of heating and quenching a silicon. In this apparatus, a rod-shaped polycrystalline silicon is placed on a supporting unit, and is heated in a heating unit. After removal from the heating unit, the polycrystalline silicon placed on the supporting unit is subjected to quenching in a quenching unit. The supporting unit is constituted of a plurality of pipes, and the polycrystalline silicon rod may be heated and quenched at a state being supported on the pipes. The quenching unit is configured such that the supporting unit supporting the polycrystalline silicon may be immersed in a water bath.
Japanese Unexamined Patent Application, First Publication No. 2005-288332 describes an apparatus of crushing a polycrystalline silicon rod. The apparatus has a heating furnace for heating the polycrystalline silicon. A supporting table to support the polycrystalline silicon rod thereon is equipped inside the heating furnace. In the configuration of the crushing apparatus, the polycrystalline silicon rod is placed on the supporting table and heated at that state. After the heating, the polycrystalline silicon rod is dropped in a water bath, thereby generating cracks in the rod.
In the method described in Japanese Unexamined Patent Application, First Publication No. 2004-91321, cracks are generated in a polycrystalline silicon by spraying a fluid such as water to a heated polycrystalline silicon, where the fluid is sprayed with a cone spray pattern or a flat fan spray pattern.
In the method described in Japanese Unexamined Patent Application, First Publication No. S60-33210, a rod-shaped polycrystalline silicon is crushed using induction heating of the rod using a micro wave. Where the polycrystalline silicon is not crushed using the micro wave, pure water is sprayed from surroundings of the polycrystalline silicon to its periphery to enhance the crushing.
Cracks may be generated in a surface and interior portion in the vicinity of the surface of polycrystalline silicon rod by heating the rod and immersing the rod in the water bath or by spraying water from the surrounding of the rod. However, since a polycrystalline silicon rod produced by the Siemens method has a diameter of, for example, 120 mm to 160 mm, it is difficult to generate cracking in a center (core) portion of the polycrystalline silicon rod, resulting in an uncracked or crack-less core portion, a so-called residual core. After the thermal shock process, the polycrystalline silicon rod is crushed to fragments by impact using hammer or the like. Where the polycrystalline silicon having the residual core is crushed to lumps of, for example, 45 mm or less in maximum length, it costs a long time for crushing the residual core portion.
Based on the consideration of the above-described circumstance, an object of the present invention is to provide a method of generating cracks in a polycrystalline silicon rod and a crack generating apparatus used in the method whereby occurrence of residual core is avoided and cracks are generated in the entire portion of the polycrystalline silicon rod, and the polycrystalline silicon rod can be crushed into small sized lumps utilizing the cracks as origins of breaking. Another object of the present invention is to provide a method of producing polycrystalline silicon lumps utilizing the method of generating cracks.